Even though smoking rates have declined in the US and in Europe, many children continue to be exposed to tobacco smoke, through secondhand or thirdhand exposure. The consequences of secondhand smoke (SHS) include increased risk of asthma, otitis media, sudden infant death syndrome, and metabolic syndrome; studies have also shown a link between SHS and decreased IQ test scores. Thirdhand smoke (THS) is a relatively new concept. When a cigarette is extinguished, components of the smoke remain in the air, and on surfaces. The tar in cigarette smoke accumulates on walls and floors, and the particulates and chemicals in cigarette smoke land on furniture, only to become airborne when someone sits down. In fact, you can see this residue on the walls of homes where smokers have lived, and it is quite impressive. Infants may be at particular risk as they crawl on the floor and then ingest the residue from their hands. Some parents believe that they are completely protecting their children when they smoke outside, however studies suggest that children of parents who smoke outside still have elevated cotinine levels. While we don’t have many studies that can directly correlate THS with increased illness, because it is hard to separate SHS and THS, children with reported THS only have cotinine levels that are associated with increased risk. Living in apartments can increase the risk of both SHS and THS exposure, as smoke travels from unit to unit, and settles on furniture and floors. Even parents who do not smoke may have children who are exposed. In the US, local and federal agencies are discussing rules that would prohibit smoking in low-income multi-unit housing, which would provide important protection for the children at highest risk.